Air traffic control is a relatively new concept. Aviation did not become widespread until the end of World War I. As the air traffic increased, a control system became necessary to avoid collisions and for pilots to determine their location and the location of the airports. Initially, the air traffic control system consisted of radio devices which the pilots used to communicate with people on the ground. With the development of radar during World War II, controllers started to use radar to track civilian and military flights and the government instituted a comprehensive air traffic control system which was deployed nationwide.
However, by the late 1960""s the air traffic control system was in disarray causing increases in delays and a general low efficiency for air travel. In addition, the system was not prepared to handle the fast growing increase in aircraft traffic which was occurring. A solution to the problem was the development of the Mode Select Beacon System (xe2x80x9cMode Sxe2x80x9d) which is a ground-air-ground data link system designed to replace the aging air traffic control system.
A method, comprising the steps of receiving a message including bits corresponding to an identifier, the identifier including a unique address for a aircraft transponder, extracting the unique address from the identifier, comparing the unique address to a set of predetermined addresses, changing selected ones of the identifier bits when the unique address is not one of the set of predetermined addresses, wherein the changing of the identifier bits changes a value of the unique address in the identifier, re-comparing the updated unique address to the set of predetermined addresses and processing the message when the unique address matches one of the set of predetermined addresses.
In addition, a system, comprising a passive radar receiving a message including bits corresponding to an identifier, the identifier including a unique address, a database including a set of predetermined addresses and a processor comparing the unique address to the set of predetermined addresses and changes selected ones of the identifier bits when the unique address is not one of the set of predetermined addresses, wherein the changing of the identifier bits changes a value of the unique address in the identifier.
Furthermore, a method, comprising the steps of receiving an in-the-clear message from an aircraft transponder at a passive ground station, the message including an identifier, the identifier including a unique address for the aircraft transponder, extracting the address from the identifier, determining whether the address has been previously stored in a set of addresses corresponding to aircraft in a range of the passive ground station, storing the address in the set of addresses when the address has not been previously stored, receiving an interrogation from an active ground station at the passive ground station, the interrogation including the unique address for the aircraft transponder and error correcting the interrogation with the set of addresses.